Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 5 de 5
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
ChemSusChem ; 13(4): 707-714, 2020 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-31912979

RESUMO

Biomass-derived surfactants with very good surface tension and critical micellar concentration properties were obtained by conversion of methyl levulinate into methyl 4-alkoxypentanoates through reductive etherification with aliphatic alcohols. Among different bifunctional acid/metal catalysts best results were obtained with Pd on carbon bearing acid sites. The reaction occurred through the formation of an enol ether intermediate followed by hydrogenation. Pd in high-density planes was the active hydrogenation species, and an optimum crystal size was found to be approximately 10 nm. The reductive etherification with aliphatic alcohols was extended to other aliphatic and cyclic ketones and aldehydes obtained from biomass, and excellent results were obtained on supported Pd catalysts with the reaction route and experimental conditions described in this work.

2.
J Am Chem Soc ; 141(49): 19304-19311, 2019 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-31774282

RESUMO

Ruthenium nanoparticles with a core-shell structure formed by a core of metallic ruthenium and a shell of ruthenium carbide have been synthesized by a mild and easy hydrothermal treatment. The dual structure and composition of the nanoparticles have been determined by synchrotron X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) analysis, and transmission electron microscopy (TEM) imaging. According to depth profile synchrotron XPS and X-ray diffraction (XRD) analysis, metallic ruthenium species predominate in the inner layers of the material, ruthenium carbide species being located on the upper surface layers. The ruthenium carbon catalysts presented herein are able to activate both CO2 and H2, exhibiting exceptional high activity for CO2 hydrogenation at low temperatures (160-200 °C) with 100% selectivity to methane, surpassing by far the most active Ru catalysts reported up to now. On the basis of catalytic studies and isotopic 13CO/12CO2/H2 experiments, the active sites responsible for this unprecedented activity can be associated with surface ruthenium carbide (RuC) species, which enable CO2 activation and transformation to methane via a direct CO2 hydrogenation mechanism. Both the high activity and the absence of CO in the gas effluent confer relevance to these catalysts for the Sabatier reaction, a chemical process with renewed interest for storing surplus renewable energy in the form of methane.

3.
ChemSusChem ; 11(17): 2870-2880, 2018 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-29975011

RESUMO

A new type of biomass-derived non-ionic surfactants has been obtained by reacting hydroxymethylfurfural (HMF), glycerol, and fatty alcohols. For instance, 5-(octyloxymethyl)furfural glyceryl acetal can be obtained in a one-pot process by etherification of HMF with fatty alcohols followed by acetalization with glycerol. For a successful solid catalyst, acidity and polarity have to be optimized to improve conversion, selectivity, and catalyst deactivation owing to the different adsorption characteristics of the reactant molecules. Accordingly, Beta zeolite with a high Si/Al ratio and practically free of connectivity defects showed good results when dealing with these biomass derivatives, which include a highly polar reactant such as glycerol. The scope of the reaction is good and a variety of new stable surfactant molecules can be obtained that present hydrophilic-lipophilic balance (HLB ) values in the range 4.9 to 6.6, which are of interest for water in oil emulsions.

4.
Chem Commun (Camb) ; 50(18): 2275-8, 2014 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-24441108

RESUMO

The first enantioselective conjugate alkynylation of ß-trifluoromethyl α,ß-enones using terminal alkynes and a taniaphos-Cu(I) complex as catalyst is described. Ketones bearing a trifluoromethylated propargylic chiral centre in the ß-position were obtained with good yields and high enantiomeric excesses (up to 99%).


Assuntos
Alquinos/química , Hidrocarbonetos Fluorados/química , Cetonas/química , Catálise , Estrutura Molecular , Estereoisomerismo
5.
Chemistry ; 20(3): 668-72, 2014 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-24339326

RESUMO

A highly enantioselective copper-catalyzed conjugate alkynylation of monoactivated enones, namely 1,1-difluoro-1-(phenylsulfonyl)-3-en-2-ones, is described. The reaction products are obtained with good yields and excellent enantioselectivities (from 92 to 99% ee). The ß-alkynylated difluoro(phenylsulfonyl) ketones can be converted into the corresponding ß-alkynylated difluoro- and trifluoromethyl ketones, esters and amides. This is the first example on the use of 1,1-difluoro-1-(phenylsulfonyl)-3-en-2-ones as substrates in an enantioselective reaction, which have been shown to be new ester/amide surrogates.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA